The present invention relates to a bridge for a stringed instrument and a stringed instrument such as an electric guitar equipped with the bridge for a stringed instrument. More specifically, the present invention pertains to a bridge for a stringed instrument that can perform alternate tuning by one-touch operation and a stringed instrument equipped with the bridge for a stringed instrument.
A stringed instrument such as a guitar is normally played in standard tuning, but occasionally tuned to alternate tuning by changing the tension of a particular string. For example, a sixth string of a guitar is normally tuned to E. However, an alternate tuning is sometimes performed by tuning the sixth string down a whole step to D, which is called a D tune. In this case, rotating a tuning peg to loosen the tension of the string tunes the string to a low pitch from a high pitch. However, it is too complicated to tune the guitar taking a long time during performance. On the other hand, it is also complicated to prepare several guitars that are tuned differently from each other.
It is further complicated in a case with a guitar equipped with a tremolo unit. In this case, even if only the sixth string is tuned a whole step down with the tuning peg, the total tension of the six strings is changed. Therefore, the force applied to the tremolo block against the tension of the strings and the tension of the string become off balance, and the tension of the five strings other than the sixth string is undesirably increased. In this case, the tension of each of the five strings must be adjusted with the tuning peg to balance the entire forces.
Therefore, a tension changing device for a stringed instrument equipped with a tremolo unit has been proposed in U.S. Pat. No. 5,359,144. The tension changing device is mounted on a guitar equipped with a tremolo unit and includes a base plate 123 as shown in FIG. 12. A flange plate 123a extends diagonally upward from the rear portion of the base plate 123. Fine tuning adjustment screws 142 are screwed into the rear end of the flange plate 123a from above and downward.
Front segments 135, each of which corresponding to one of strings, are secured to the front portion of the base plate 123. Each front segment 135 rotatably supports a rear segment 137 via a support shaft 138. The proximal end of each string 115 is retained between the corresponding rear segment 137 and a clamping block 139 located in the rear segment 137. Therefore, the rear segments 137 are urged forward (toward a head) by the tension of the strings 115 with the base plate 123.
Knife edges 129 are formed at the front end of the base plate 123. Each knife edge 129 is engaged with a stud bolt 131 secured to a body so that the base plate 123 is tiltably supported by the body. A tremolo block 145 (partially shown in FIG. 12) is located below the base plate 123. The tremolo block 145 is urged forward of the body by coil springs (not shown). Therefore, since the base plate 123 is tiltably held by the balance between the tension of the strings 115 and the force of the coil springs, the base plate 123 is tilted by manipulating a tremolo arm 130.
A shank 190, which extends rearward, is secured at the rear end of each rear segment 137. The shank 190 extends rearward through the flange plate 123a and the rear end of the shank 190 is coupled to a shifting member 191. The shifting member 191 can be shifted forward and rearward while the shank 190 is loosely fit inside. Each rear segment 137 and the corresponding shank 190 are urged forward of the body by the tension of the corresponding string 115. Therefore, the shifting member 191 is also urged to rotate counterclockwise about the support shaft 138 as viewed in FIG. 12. Therefore, in a state shown in FIG. 12, an upper flat surface 191a of the shifting member 191 abuts against the lower end of the corresponding fine tuning adjustment screw 142 located above the upper flat surface 191a. 
A leaf spring 192 is secured to the lower surface of the base plate 123. The rear end of the leaf spring 192 abuts against the lower surface of the shifting member 191. Therefore, the shifting member 191 is urged upward by the leaf spring 192. In this state, for example, the sixth string is tuned to E by rotating the corresponding tuning peg on the head, and fine tuning can further be performed by rotating the fine tuning adjustment screw 142 as required.
Next, a case where the sixth string 115 is tuned down a whole step to D from the state shown in FIG. 12 will now be described with reference to FIG. 13. At first, the shifting member 191 is held by hand and pulled rearward so that the shifting member 191 is shifted rearward. Then, the distal end of the corresponding leaf spring 192 is fitted in an engaging recess 191b formed at the front end of the lower surface of the shifting member 191, and the shifting member 191 is fixed. At this time, the corresponding rear segment 137, the shank 190, and the shifting member 191 are urged counterclockwise as viewed in FIG. 12 by the tension of the string 115 about the support shaft 138. Therefore, the upper flat surface 191a of the shifting member 191 is disengaged from the lower end of the fine tuning adjustment screw 142. The lower end of the fine tuning adjustment screw 142 then abuts against the shank 190. Accordingly, the rear segment 137, the shank 190, and the shifting member 191 are rotated counterclockwise about the support shaft 138 by a predetermined thickness of the shifting member 191. As a result, the tension of the sixth string 115 is reduced and the sixth string 115 is tuned to D from E. Thus, according to the U.S. Pat. No. 5,359,144, a bridge for a stringed instrument that is not equipped with the tremolo unit can perform alternate tuning by shifting the shifting member 191 rearward. Also, according to such a bridge for a stringed instrument, the string 115 can be automatically tuned back to E by returning the fine tuning adjustment screw 142 to the state shown in FIG. 12.
On the other hand, according to the bridge for a stringed instrument equipped with the tremolo unit, even if the device of FIG. 12 is applied, the total tension of the six strings is reduced by the influence of the sixth string that has been adjusted to reduce its tension. Therefore, the force of the spring of the tremolo unit and the tension of each string become off balance. Therefore, since the tension of each of the first to fifth strings is increased, the tension of each of the five strings must be adjusted again. Thus, according to the tremolo unit of the above publication, after performing alternate tuning with the shifting member 191, the force of the spring for the tremolo unit must be manually adjusted to regain the balance of the entire tremolo unit.
However, according to the above mentioned bridge for a stringed instrument, when performing alternate tuning using the shifting member 191, the sixth string 115 cannot be guaranteed to be correctly tuned to D due to the property of the sixth string 115 itself and the influence of the entire tension even if the accuracy of the shifting member 191 is increased. Therefore, it is possible to tune the sixth string 115 to approximately D, but the sixth string 115 must be correctly tuned by manipulating the fine tuning adjustment screw 142 before playing the guitar. Furthermore, when tuning the sixth string 115 back to E by pressing the shifting member 191 forward after correctly tuning the sixth string 115 to D, the tuning state becomes inaccurate and the sixth string 115 cannot be restored to E. Such a problem occurs with a bridge that is not equipped with the tremolo unit.
In addition, according to the bridge equipped with the tremolo unit, even if the sixth string is accurately adjusted, the entire balance goes wrong. Therefore, according to the conventional unit shown in FIG. 12, it is possible to tune all the strings at the same time, but each string must be fine-tuned manually before playing the guitar. Thus, the adjustment procedure is complicated.
Furthermore, in the above mentioned invention, the shifting member 191 projects rearward of the body. Therefore, when the tremolo arm 130 is pulled upward, a space is necessary so that the shifting member 191 do not interfere with the body. Particularly, as shown in FIG. 13, when the sixth string 115 is tuned to D, the shifting member 191 further projects rearward by a large amount. Thus, a large space is required between the body and the shifting member 191. Therefore, the above described tremolo unit requires a special body and cannot be replaced with the conventional tremolo unit. That is, the tremolo unit of the above publication lacks versatility.